An opposed-piston, opposed-cylinder (OPOC) is disclosed in U.S. Pat. No. 6,170,443, which is incorporated herein in its entirety. The configuration in '443 has an asymmetrical arrangement of the pistons. That is, in one of the cylinders, the intake piston, i.e., that piston that uncovers intake ports, is located closer to the crankshaft than the exhaust piston. In the other cylinder, the exhaust piston is located closer to the crankshaft than the intake piston. Such an arrangement provides some distinct advantages such as nearly perfect balancing of the engine. However, some small detractors result due to the asymmetric arrangement and the phase offset between the intake and the exhaust pistons, the offset being provided for scavenging purposes. In particular, the crankshaft is a split-pin design. That is, the journals of the crankshaft, to which the pistons of the two cylinders couple, cannot be smooth cylinders to which two connecting rods couple, but instead includes two cylindrical crankpins that are offset from each other (as shown in FIGS. 9 and 10b in '443). This is a more costly and less robust design than the simpler single cylindrical journals to which two connecting rods couple. The highest stress location in a crankshaft tends to be located at the interface between the journal and the web portion of the crankshaft. There are techniques that can be used to harden that portion of the crankshaft such as: induction hardening or rolling. These are difficult and expensive for a split-pin design.
Additionally, as the inner pistons couple to the crankshaft in a different manner than the outer pistons, the '443 engine has four distinctly different pistons: an inner intake piston, an outer intake piston, an inner exhaust piston, and an outer exhaust piston. To reduce engineering costs, manufacturing costs, and complexity, it is desirable to have as few different parts as possible. Other detractors include optimizing two combustion chamber shapes and port heights, i.e., one for each of the two cylinders. One combustion chamber is formed by an inner intake piston and an outer exhaust piston and the other is formed by an outer intake piston and an inner exhaust piston. Part of the reason for the inconsistency from one cylinder to the other cylinder is due to differences in the flow characteristics by virtue of the asymmetric nature of the induction and exhaust systems.
To overcome these detractors, an OPOC with a symmetrical arrangement of the pistons is disclosed in U.S. Pat. No. 7,469,664, which is incorporated herein in its entirety. The two cylinders of the OPOC in '664 are collinear meaning that that the central axes of the two cylinders lay on essentially the same line. In the engine in '664, two connecting rods, that mesh together, couple to a single journal; this arrangement is commonly referred to as a forked rod design. Because the forked rod must be slid over the journal, the crankshaft is a “build-up”, meaning that it is assembled of multiple parts with the final assembly accomplished after the connecting rods have been installed. Such a crankshaft is more expensive to manufacture and assemble.
To overcome issues associated with a multi-piece crankshaft, alternative coupling strategies for inner pistons and for outer pistons are disclosed in commonly-assigned, published U.S. applications: 2012/0207415 A1 filed 3 Feb. 2012 and 2012/0247419 A1 filed 2 Apr. 2012. Although such disclosed solutions provide many advantages for the OPOC engine and provide the desired symmetrical arrangement of the pistons, these coupling arrangements are unique in the industry and are to date untested. For production purposes in the nearer term, some manufacturers prefer to use technologies that are well developed and thus are reticent to adopt the coupling arrangements disclosed in applications '415 and '419 until further proven.
An advantageous OPOC configuration, according to some embodiments disclosed herein, relies on proven mechanical technologies, provides a symmetric arrangement of the pistons, and uses a unitary crankshaft.
An internal combustion engine is disclosed that includes a unitary crankshaft, a block into which the crankshaft is mounted, the block defining two cylinders wherein a first of the two cylinders is arranged substantially opposite a second of the two cylinders with respect to the crankshaft and a central axis of the first cylinder is offset from a central axis of the second cylinder by a predetermined distance, a first intake piston and a first exhaust piston inserted into the first cylinder with the first exhaust piston closer to the crankshaft than the first intake piston, and a second intake piston and a second exhaust piston inserted into the second cylinder with the second exhaust piston closer to the crankshaft than the second intake piston. The engine has a first pushrod that couples between a central journal of the crankshaft and the first exhaust piston; and a second pushrod that couples between the central journal of the crankshaft and the second exhaust piston wherein the first pushrod and the second pushrod are adjacent to each other and the predetermined distance that the cylinders are offset is substantially equal to a distance between the pushrods taken along an axis of rotation of the crankshaft.
In some embodiments, a first pair of shell bearings are placed on the central journal with the first pair of shell bearings located between the central journal and the first pushrod and a second pair of shell bearings placed on the central journal with the second pair of shell bearings located between the central journal and the second pushrod wherein the first pair of shell bearings is adjacent to the second pair of shell bearings. Alternatively, a single part of shell bearings are placed on the central journal with the first and second pushrods are coupled to the outer surface of the shell bearings. In some embodiments, at least one of the pair of shell bearings includes an outwardly extending tab; the first pushrod has a pocket defined on a surface of the first pushrod that nests with the shell bearings; and the tab engages with the pocket.
The crankshaft has at least five journals: a central eccentric journal, a front eccentric journal, a rear eccentric journal, a front main journal having an axis of rotation collinear with an axis of rotation of the crankshaft, and a rear main journal having an axis of rotation collinear with the axis of rotation of the crankshaft. The engine also includes: a first rear pullrod that couples between the rear journal of the crankshaft and the first intake piston, a first front pullrod that couples between the front journal of the crankshaft and the first intake piston, a second rear pullrod that couples between the rear journal of the crankshaft and the second intake piston, and a second front pullrod that couples between the front journal of the crankshaft and the second intake piston. In some embodiments, the engine further includes: a first rear pair of shell bearings placed on the rear journal with the first rear pair of shell bearings located between the rear journal and the first rear pullrod, a second rear pair of shell bearings placed on the rear journal with the second rear pair of shell bearings located between the rear journal and the second pullrod wherein the first rear pair of shell bearings is adjacent to the second rear pair of shell bearings, a first front pair of shell bearings placed on the front journal with the first front pair of shell bearings located between the front journal and the first front pullrod, and a second front pair of shell bearings placed on the front journal with the second front pair of shell bearings located between the front journal and the second pullrod wherein the first front pair of shell bearings is adjacent to the second front pair of shell bearings. Some embodiments include a rear pair of shell bearings placed on the central journal wherein the first and second rear pullrods are coupled to the outer surface of the rear pair of shell bearings and a front pair of shell bearing placed on the central journal wherein the first and second front pullrods are coupled to the outer surface of the front pair of shell bearings. In some alternatives, at least one of the rear pair of shell bearings includes an outwardly extending tab; the first rear pullrod has a pocket defined on a surface of the first rear pullrod that nests with the shell bearings; the tab associated with the rear pair of shell bearings engages with the pocket associated with the first rear pullrod; at least one of the front pair of shell bearings includes an outwardly extending tab; the first front pullrod has a pocket defined on a surface of the first front pullrod that nests with the shell bearings; and the tab associated with the front pair of shell bearings engages with the pocket associated with the first front pullrod.
The crankshaft in some embodiments the crankshaft is a unitary or one-piece crankshaft. The front and rear eccentric journals have a substantially identical crank throw and substantially equal phasing. The central journal has a crank throw greater than the crank throw of the front and rear eccentric journals and is offset between 150 to 180 degrees with respect to the front and rear eccentric journals.
Also disclosed is an internal combustion engine having a unitary crankshaft, a block into which the crankshaft is mounted, the block defining two cylinders wherein a first of the two cylinders is arranged substantially opposite a second of the two cylinders with respect to the crankshaft, two substantially identical inner pistons, one of which is inserted into the first cylinder and the other of which is inserted into the second cylinder, and two substantially identical outer pistons, one of which is inserted into the first cylinder and the other of which is inserted into the second cylinder wherein the inner pistons are located nearer the crankshaft than the two outer pistons. In some alternatives, a central axis of the first cylinder is offset from a central axis of the second cylinder by a predetermined distance. A first pushrod couples between a central journal of the crankshaft and the inner piston in the first cylinder. A second pushrod couples between the central journal of the crankshaft and the inner piston in the second cylinder. The first pushrod and the second pushrod are adjacent to each other and the predetermined distance that the cylinders are offset is substantially equal to a distance that first and second pushrods are displaced from each other taken along a central axis of the crankshaft.
The two inner pistons are exhaust pistons and the two outer pistons are intake pistons in one alternative. In another alternative, the two inner pistons are intake pistons, and the two outer pistons are exhaust pistons.
A plurality of ports are defined in each of the two cylinders with an inner plurality of ports that are located a first predetermined distance from the crankshaft and an outer plurality of ports that are located a second predetermined distance from the crankshaft with the second predetermined distance being roughly double the first predetermined distance. The engine further includes a first manifold system fluidly coupled to the inner plurality of ports and a second manifold system fluidly coupled to the outer plurality of ports. In some embodiments, the first manifold system is an intake system and the second manifold system is an exhaust system. In other embodiments, the first manifold system is an exhaust system and the second manifold system is an intake system.
In another embodiment, an engine has a crankshaft and a block into which the crankshaft is mounted. The block defines two cylinders with a first of the two cylinders arranged substantially opposite a second of the two cylinders with respect to the crankshaft and a central axis of the first cylinder is offset from a central axis of the second cylinder by a first predetermined offset. The engine includes: a plurality of inner ports defined in the first cylinder with an inner edge of the inner ports located at a first predetermined distance from the crankshaft and an outer edge of the inner ports located at a second predetermined distance from the crankshaft, a plurality of inner ports defined in the second cylinder with an inner edge of the inner ports located at the first predetermined distance from the crankshaft and an outer edge of the inner ports located at the second predetermined distance from the crankshaft, a plurality of outer ports defined in the first cylinder with an inner edge of the outer ports located at a third predetermined distance from the crankshaft and an outer edge of the outer ports located at a fourth predetermined distance cylinder from the crankshaft, and a plurality of outer ports defined in the second cylinder with an inner edge of the outer ports located at the third predetermined distance from the crankshaft and a outer edge of the outer ports located at the fourth predetermined distance from the crankshaft. In some embodiments, the engine further includes: a plurality of outermost ports defined in the first cylinder with an inner edge of the outermost ports located at a fifth predetermined distance from the crankshaft and an outer edge of the outermost ports located at a sixth predetermined distance from the crankshaft and a plurality of outermost ports defined in the second cylinder with an inner edge of the outermost ports located at the fifth predetermined distance from the crankshaft and an outer edge of the outermost ports located at the sixth predetermined distance from the crankshaft.
In some embodiments: the pluralities of inner ports are exhaust ports; the pluralities of outer ports are primary intake ports; the plurality of outermost ports is secondary intake ports; and all ports are shaped substantially as one of: a rectangle, a parallelogram, an oval, and a circle.
The various disclosed embodiments include one or more of the following advantages:    a crankshaft without split pins;    identical left and right cylinder blocks;    only first-order unbalanced forces that can be overcome by weighting of the crankshaft such that the center of gravity is offset with respect to the axis of rotation of the crankshaft;    symmetric arrangement of the pistons with common inner pistons and common outer pistons, i.e., two each of two piston designs as contrasted to some prior designs that had one each of four piston designs;    the intake and exhaust flanges and ports are symmetrical;    coupling of connecting rods to the journals draws upon well-known technologies used in the industry for decades;    a stiffer, unitary crankshaft as contrasted with a built-up crankshaft or split-pin crankshafts used in some prior designs; and    substantially identical combustion chamber configurations in the two cylinders.